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48

Drawbacks.

some parts of a pattern by lifting portions of sand on
' drawbacks} An example often quoted, and a very goo
purposes of explanation, is that of a lathe bed.

Fig. 62a shews a section of the pattern lying in th
The bed is reversed, so that the planed surfaces shall be

N,   PRTTCFIN  D/V/DED  AT

scum; and these surfaces are in the pattern made loose piei
The upper portion of the pattern can be easily removed, fc
problem is to withdraw the pieces a a. This can only be ac
by building the sand at b b on plates cc^ provided with hand
which they and the sand upon them may be removed, afl